1. Field of the Invention
The present invention relates to a method of extracting a circular region from a fringe image. The method extracts, on a coordinate system having captured a fringe image carrying phase information such as the surface form and internal refractive index of a sample having a circular region to be analyzed within an area to be observed, a circular image region representing the region to be analyzed.
2. Description of the Prior Art
Recently, research and development of optical fibers for use in optical communications has been vigorously under way. Known as an example of this kind of optical fibers is one comprising a core having an outer diameter of about 10 μm and a cladding layer, disposed at the outer periphery thereof, having an outer diameter of about 125 μm, for example, and further comprising a ferrule, disposed at a connecting end part thereof, for connecting the optical fiber to another optical fiber.
The ferrule is a cylindrical component, constituting an optical connector, for holding and securing one end of the optical fiber in order to connect it to another optical fiber. After an optical fiber is inserted and secured with an adhesive or the like to the center part of the outer diameter of a ferrule, the leading end of the ferrule is polished into a mirror surface, so that two optical fibers held by respective ferrules can be connected to each other when the leading end faces of the two ferrules are butted against each other.
While the leading end face of a ferrule has been known to be polished into a plane perpendicular to the optical axis or a plane obliquely intersecting the optical axis, attention has recently been directed to one whose leading end face is subjected to PC (physical contact) polishing so as to attain a convex spherical form such that the leading end face is elastically deformed by a pressure for butting the leading end faces of ferrules against each other.
For reducing the optical loss occurring when optical fibers are connected to each other, various high-precision specs for ferrules have been defined by JIS (Japanese Industrial Standard). For the PC-polished ferrule, six μm-order specs such as dimensional errors in the radius of curvature of the leading end face and positional deviation errors between the apex of the spherical leading end face of the ferrule and the center of the core of the optical fiber (the center of the fiber outer form) have been defined.
There are cases where a microscopic interferometer apparatus (also known as “interferometric microscope”) is used for inspecting whether a produced ferrule conforms to the above-mentioned specs or not. The microscopic interferometer apparatus is configured such that interference fringes formed by interference between object light carrying phase information such as the surface form and refractive index distribution of a minute sample and reference light reflected by a predetermined reference plate are observed, and forms and changes of the interference fringes are measured and analyzed, so as to obtain the phase information of the sample.
When inspecting a manufactured ferrule by using such a microscopic interferometer apparatus, it is necessary to extract a circular image region representing an area of an optical fiber on a coordinate system having captured a fringe image of an area to be observed in a ferrule.
Conventionally known as a method of extracting such a circular image region is one in which, while a template corresponding to a reference size on a coordinate system having captured the fringe image (the size corresponding to the core region of the optical fiber in the coordinate system) is moved little by little on the coordinate system, an image region coinciding with this template is identified as the circular image region.
However, such a conventional circular region extracting method has been problematic in that it takes time to extract the circular image region, since the template must be moved little by little on the coordinate system over all the image area having captured the fringe image.